#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
#define ull unsigned long long
ull int c[55][55];
void init()
{
    c[0][0] = 1;
    c[1][0] = 1;
    c[1][1] = 1;
    for(int i = 2;i<55;i++)
    {
        c[i][0] = 1;
        c[i][i] = 1;
        for(int j = 1;j<i;j++) c[i][j] = c[i-1][j-1]+c[i-1][j]; 
    }
}
int main()
{
    init();
    int n,a,b;
    cin>>n>>a>>b;
    ull ans = 0;
    for(int i = 0;i<=a;i++)
    {
        for(int j = 0;j<=b;j++)
        {
            ans += c[n][i]*c[n][j];
        }
    }
    cout<<ans<<"\n";
}
